Method for producing phosphorus



y 1 19 2- E. H. 'BUFORD 2,289,538

METHOD FOR PRODUCING PHOSPHORUS Filed Oct. 13, 1939 I5 ELECTRQQE a 4 1;, 5 GAS m1- FURNACE 1 3 ,(5 WHOLE E. H. BUFORD INVENTOR AWM ATTORNEY Patented July 14, 1942 UNITED STATES PATENT OFFICE METHOD FOR PRODUCING PHOSPHORUS Edwin H. Buford, St. Louis, Mo., assignor to Monsanto Chemical Company, a corporation of Delaware Application October 13, 1939, Serial No. 299,242

7 Claims.

This invention relates to a method and apparatus for producing phosphorus by a process in- Other reactions may of course take place in the furnace between the constitutents charged thereto, as it is well recognized that the materials entering the furnace contain associated impurities such as iron oxide, alumina, moisture, hydrocarbons, carbonates, fluorides, etc., however for the understanding of the present invention these above-mentioned impurities with the exception of moisture need not be further considered except to recognize their presence in the burden.

The principal products of the reactiontgiven above as far as their physical state is concerned are seen to be a gaseous product and a liquid (slag) product. The gaseous product will consist chiefly of the vapor 'of phosphorus, P4, and carbon monoxide, CO. Some phosphine, PHa, may also be present in the gaseous product, the source of which probably is a reaction between phosphorus and water vapor or moisture. The slag product consists of the non-volatile residue, including the lime; silica, alumina, iron compounds of phosphorus, etc. The slag product in molten form is removed from the furnace through a slag tap-hole.

The gaseous product leaves the furnace through a gas exit in the roof and may be further treated for removal of impurities, after which it is cooled in order to condense the vapor of phosphorus therein to recover the same in liquid form. 1

For efficient trouble-free operation of the furnace and the process described herein, it is highly desirable that the furnace and stock-feeding mechanism be maintained free of air and oxidizing gases generally. The presence of oxygen within the furnace, from whatever source derived, will combine with the phosphorus, phosphine and carbon monoxide yielding phosphoric anhydride, (P205) carbon dioxide and water. The former will hydrate by reaction with moisture inthe phosphine, forming gummy metaphosphoric acid which then depositsupon the interior of the furnace, particles of stock, stock feed pipes and electrode mechanism making operation difficult in addition to lowering the output of phosphorus from the furnace. The oxidation of the carbon monoxide may at times take place with explosive violence with danger to operators and equipment. The presence of excessive quantities of phosphine may at times cause spontaneous ignition to take place.

I have now found that the above-mentioned difficulties may be largely overcome by supplying evitably present in the burden or formed from to the phosphorus furnace a non-oxidizing or inert gas. Such inert gas is supplied preferably continuously to the stock feeding mechanism appurtenant to the furnace and especially do I find it advantageous to maintain the pressure of such inert gas supplied to the stock feeding mechanism at a higher value than the pressure prevailing in the furnace itself.

In view of the fact that the furnace burden usually supplied to the phosphorus furnace is comprised of granular particles such as pebble phosphate ores, phosphatic sinter or nodulized phosphatic ores, together with particles of coke and silica, I have found that the entrance of such granular burden carries mechanically within the interstices thereof and adsorbed thereon, a certain amount of air, which ordinarily may account for a considerable amount of oxidation of phosphorus, phosphorus compounds and carbon monoxide, as above explained. According to my present invention I may supply to said burden as it gravitates, or is mechanically conveyed to said furnace a current of inert gas, at a pressure higher than that prevailing in said smelting furnace'and divide the flow thereof, causing a part ofsaid inert gas to flow downwardly into said furnace, while the remainder flows upwardly through the gravitating stock removing thereby the greater part of the entrained air and then discharging the inert gas and the entrained air diffused therein exteriorly of the feeding system.

My invention may be described by reference to the accompanying drawing, the single figure of which illustrates diagrammatically the essential features of my invention.

In the drawing, I indicates a phosphorus furnace provided with electrode 2, slag tap hole 3, gas exit 4 in the roof 5 of furnace 'l and a plurality of stock feed pipes of which only two are shown numbered 6 and l.

The phosphatic burden 8 is supplied from source not shown by means of s cking belt conveyor 9 to the hopper of a stock gate lock ill, by which the stock or burden may be locked into stock bin l l with a minimum of loss of inert gas from said stock bin ll. Stock bin ll will at all times during operation contain a quantity of burden, which may be discharged by means of pipe l2 into enclosed conveyor l3 thence into inert gas to pipe i8 and control valve i9 and thence flows by means of pipe 20 into stock bin II at a predetermined pressure above that existing in the furnace atmosphere of furnace I. When this condition is maintained a part of the inert gas may be made to pass downwardly concurrently with the burden from the bin ll into pipe l2, conveyor 13 furnace feed bin M and feed pipes 6 and I, all of which equipment is made substantially gas tight, as is also the stock bin II and the furnace I. The flow of inert gas passing from bin i l by the means described into the interior of furnace I, serves to prevent entrance of phosphorus bearing gases into the stock fe'ed pipes 6 and 1. Ordinarily some leakage of inert gas contained within the enclosed space of stock bin ll, occurs througn the locking gates, which leaking gas serves to carry with it some of the entrapped air carried in the interstices of the stock and adsorbed thereon. However since the locking gates do not operate continuously, but only when the furnace stock bin is being filled, a certain concentration of air may collect within the upper zone of stock bin ii which is undesirable. I therefore provide a positive controllable exit for bleeding inert gas from said bin by providing pipe 22 connecting with the upper zone of said bin H which pipe 22 may be provided with throttle valve 23, or other suitable device for controlling the flow of purging gas from within stock bin II to the external atmosphere. In practice, I find it convenient to adjust the flow of inert gas leaving stock bin H by means of pipe 22 to the point where chemical test of the gas in said pipe shows substantial absence of oxygen. Thereafter, pressure cont' cl valve l9, actuated electrically or mechanical]; by the differential controller I serves to keep the gas pressure in bin H sufficiently above the pressure in furnace i so thata portion of said inert gas flows concurrently with said downward flowing stock and effectively prevents the phosphorus containing furnace gases from entering into the stock feed pipes 3 and i.

By introducing the flow of inert gas into a lower zone of stock bin i I, I am enabled to effect a countercurrent flow of such gas relative to the gravitating stock in said bin, an effect which'is conducive to the substantially complete removal of air from said stock. At the same time I am assured of the complete sweeping out of air from the opper zone of said bin a condition practically assuring the safety of the entire installation against explosion hazards.

From time to time during the operation of the phosphorus furnace pressure changes of the furnace atmosphere occur occasioned by uncontroliable gas evolution from the smelting zone. At times these pressure increases may reach app'reciable values.- By means of the differential pressure controller [6, I provide that the pressure of the inert atmosphere within bin II increases at substantially the same rate as does that of the furnace atmosphere and is always maintained at a predetermined excess pressure, say to 1" of water, over that existing in the furnace, thereby providingfor a substantially constant flow of inert gas into said furnace together with the descending stock.

Differential pressure controller l6 provides pressure responsivemeans controlling the pressure of gas in the stock bin H by actuating control means l9, regulating the supply of inert gas entering said stock bin II, and at the same time provides means for maintaining the pressure in said stock bin above that existing in the furnace atmosphere with which said bin communicates.

By the means described I provide one single bin II for storing and deairing the furnace burden. Feed bin ordinarily is not considered as a stock storage bin and in fact functions only as a distributing bin for the furnace burden. It may be replaced by other stock distributing means.

Due to the fact that my invention may be applied to various phosphorus smelting furnaces operatingupon-phosphatic ores of different types, it is impossible to give numerical values for the various pressures employed, in fact the determination of desirable pressure is well within the capabilities of one skilled in the art.

The inert gas employed in the operation of my device may be nitrogen or carbon dioxide gas or a mixture of the two. It may be produced by the burning of combustible gas with the optimum quantity of air so that the gas obtained will contain only carbon dioxide and nitrogen and none or only small amounts of oxygen and carbon monoxide. By the term inert I mean that it is practically inert with respect to the gaseous products encountered in the phosphorus smelting operation.

The gas pressure within furnace I may be substantially the same as that of the external atmosphere but for most satisfactory operation I prefer to keep such furnace gas pressure at a value in excess of that of the surrounding atmosphere. A value of from of water to as much as 2" or 3" of water may advantageously be employed.

What I claim is:

1. The improvement in the art of operating an enclosed phosphorus smelting furnace in which a phosphatic smelting burden mixed including carbon is supplied to said furnace by flow through and from a burden feed bin, and to which burden feed bin said smelting burden mixed with air is supplied, comprising supplying to said burden feed bin and to said burden therein a supply of inert gas to produce-in said bin a super-atmospheric pressure, and venting from said bin a portion of said inert gas admixed with air, said portion thus vented being sufiicient in amount to remove from said burden substantially all of said air.

2. The improvement in the art of operating an enclosed phosphorus smelting furnace in which a phosphatic smelting burden, including carbon, is supplied to said furnace by gravitational flow responsive to the demands of said furnace, from aburden feed bin having an upper and a lower zone, to the upper zone of said bin, said smelting burden admixed with gaseous oxygen is supplied, comprising supplying to said burden feed bin an inert gas to produce in said bin a pressure somewhat above atmospheric pressure, and venting from said upper portion of wherein said burden admixed with mechanically entrapped air is supplied to said bin, comprising supplying to said enclosed bin an inert gas to produce in said bin a gas pressure in excess'of that of said furnace atmosphere, venting from said bin' a portion of said inert gas, said portion of gas vented being sufi'icient to carry therewith substantially all of said air.

4. The improvement in the process of operating an enclosed phosphorus smelting furnace, in

which process said furnace is supplied with a smelting burden mixed with cokefrom an enclosed burden feed bin having upper and lower Zones, and wherein said burden, admixed with air is supplied to said upper zone, and said furnace is supplied with burden from said lower zone, and wherein said furnace during operation contains a furnace atmosphere under slight super-atmospheric pressure, comprising supplying to said bin intermediate said upper and lower zones an inert gas to produce in said bin a gas pressure in excess of that of said furnace atmosphere, and venting from said upper zone a portion of said inert gas in amount sufficient to remove from said burden substantially all of said air. v 5. The improvement in the process of operating an enclosed phosphorus smelting furnace, in which process said furnace is supplied'with a smelting burden mixed with coke from an enclosed burden feed bin provided with upper and lower zones, and in which bin said burden flows downwardly from said upper to said lower zone, responsive to the demands of said'furnac'e, and wherein said bin is supplied with a smeltirg burden admixed with entrapped air; comprising thereto and communicating therewith, with aintroducing into said burden a supply of inert gas, flowing a portion of said gas counter-current to said burden flow and venting a suflicient portion of said inert gas to remove from said burden substantially all of said air.

6. The improvement in the process of operating an enclosed phosphorus smelting furnace, in which process said furnace is supplied, from an enclosed-burden feed bin adjacent thereto and communicating therewith, with a smelting burden including coke, and which bin is provided with upper and lower zones, and'in which bin said burden flows downwardly from said upper to said lower zone, responsive to the demands of said furnace, and wherein said upper zone of said bin is supplied with said smelting burden admixed with air, which improvement comprises introducing an inert gas into said burden feed bin in amount togproduce a slight super-atmos-;

pheric pressure therein, flowing a portion of said inert gas countercurrent to said flow of burden and venting said portion from said bin, said amount thus vented being suflicient in amount to remove from said burden substantially all of said admixed air, while flowing another portion of said inert gas concurrent to said flowing burden, said concurrent flowing gas passing into said furnace.

7. The improvement in the process of operating an enclosed phosphorus smelting furnace in which process said furnace is supplied, from an elevated enclosed burden feed bin adjacent smelting burden including carbonaceous matter, and in which process said furnace is operated under slight super-atmospheric pressure, said bin being provided with upper and lower zones,

and in which bin said burden flows downwardly.

from said upper to said lower zone, responsive to the demands of said furnace,'and wherein said upper zone is supplied with said burden admixed with air, which comprises supplying to said bin intermediate the said upper and lower zones thereof, a flow of inert gas to produce in saidbin a pressure in slight excess over said furnace pressure, venting a portion of said inert gas, said portion vented containing substantially all of said air, while flowing another portion thereof concurrent with said burden flow into said furnace.

EDWIN H. BUFORD. 

